Process for recovering nitrogen-oxide vapors



Patented lane 23, T23.

PHILIPPE AUGUSTE GU'YE, OF GENEVA, SWITZERLAND, ANDYALBERT SCHMIDT, OF PARIS, FRANCE, ASSIGNORS T0 LAZOTE FRANCAIS, S. A., OF PARIS, FRANCE.

PR0G%S I,I1 FOE RJECOVERING NITROGEN-OXIDE VAPORS.

No Drawing.

To all whom it may concern:

Be it known that we, PHILIPPE .Aoos'rs GUYE, a citizen of the Confederation of Switzerland, an A'Lnnn'n SCHMIDT, a citizen of the Republic of France, residing at Geneva, Switzerland, and Paris, in the Republic oii France, have invented certain new and useful Improvements in Processes for Recovering Nitrogen-Oxide Vapors, of which the following is a specification.

The object of the present invention is a process for recovering nitrogen oxide vapors mixed with dry gases by means of alumina.

The experience on which the present in- I vention is based, has proved, that if alumina A1 0 is preparedin a perfectly anhydrous state, it gets the property to very easily absorb dry nitrous vapors (a mixture of NO and N 0 thereby giving an addi tion prodpet (complex salt) approximately corresponding to the formula 2(Al,0,)NO

. in the case. of gash) Withthe gas N 0 the complexity, is analogous. The lower temperature at which the alumina has been dehydrated the more readily will the nitrogen oxide gases be adsorbed thereby, and good results are obtained, if the temperature at which the water is extracated, does not exceed 400 (3. It is however possible to go even lower with the temperature it th alumina is dehydrated in a vacuum.

The addition products between A1 0 and the nitrous vapors, if heated to about 100, will evolve all these vapors, for instance the dissociation tension of -the compound MALOQNU, is at. 71 C. about 1 atmosphere. I

Ti alumina which has been dehydrated as said above is'treated with dry gases containing very diluted nitrousvapors (such as they are obtained for instance in the manufacture of synthetic. nitric acid with are furnaces acting upon a dry mixture of nitrogen and oxygen), one needs only to bring the temperature of flreaction below 20? C. in order to realize a nearly complete absorption of these nitrous vapors. The dissociation tension of the above complex (ALOQNU, is for instance 1 mm. of mercury at 20 (3., or 0.1 mm. at' -0 C. or 0.007 mm. at -40 C. The absorption s therefore practically complete between new According to theinvention these gases of Application and July 8, 1920. serial in. 394,250.

-30 and 40 C. withthe gases in which the volume of NO l "/0. i

The process for recovering the nitrous vapors that are mixed with dry gases, which does not exceed toprocess is the subject of the" present; lIl'VBIb i tion, is based upon the knowledge of these data.

a temperature which is between the ordinary temperature and -80 C. are directed upon anhydrous alumina, from which the water had been extracated at a low, tempera: ture. The additional product formed between the alumina :and the nitrous vapors is then heated in order to dissociate it and to evolve these vapors in a pure and concen' trated state.

One may for. instance proceed in the following manner: The dry gases containin nitrousvapors which are to .be recovere portion of N 0 the respective temperature may be lowered to -50 .CQand even: as far The addition product which is obtained in the above manner is then heated to a temperature exceeding 70 0. and being generally between 70 and 120 C. The nitrous vapors are condensed or collected in the usual way. If the nitrous vapors submittedto reaction with A1 0 do only contain gas N0 this gas would be regenerated into a pure state. i

-' F or contmuous operation two similar devices aremade use of for'- proceeding as above described.- Each one of the two devices absorb and evolve t h'enitrous gases alternatively.

Both operations (absoibin g by; A1 0 ataevolving nitrous vapors) can be carried out in the same apparatus. It is also possible to lower. the temperature at which the nitrous vapors are evolved by keeping up a partial vacuum in the apparatus in which the complex salt is heated.

After having at a temperature of C. recovered all the nitrous vapors contained in an'arc gas of a yield of 0.5 to 1.0% it suffices to heat the mixture to +40 C. in a vacuum of 200 mm. in order to evolve the nitrous gases.

In the course of time it may happen that besides these additional products and traces of humidity which penetrate into the apparatus, hydrated nitrates ofaluminium are formed, which subsequently will paralyze the absorption of oxides of nitrogen. lt is in such a case only necessary to heat the mass to about 400 in order to recuperate'the peroxide and to regenerate the alumina from which the water is'tully extracted and su1table to work the same as before.

We claim as our invention:

1. A process for recovering nitrogen oxide vapors mixed with dry" gases comprising condensing them with anhydrous alumina obtained .by dehydrating hydrous alumina at substantially not above 400 C.

2. A process for recovering nitrogen oxide vapors mixed with dry gases, comprising condensing them with anhydrous alumina obtained by dehydrating hydrous alumina at substantially not above 400 C., said vapors being directed at a teniiperature between normal and C. upon said anhydrous alumina.

3. A process for recovering nitrogen. oxide vapors mixed with dry gases, con'lprisingcont'lensing them with anhydrous ahnnina obtained by dehydrating hydrous alumina at substantially not above 400 said vapors being directed at a temperature belwccn normal and S0 (J. upon said anhydrous alumina, and then heating to dissociate the nitrogen oxide from the alumina.

l. A process for recovering nitrogen o apors mixed with dry gas s conipri if condensing them with anhydrous alumina obtained by dehydrating hydrous alumina at substantially not above (I, said rapors being directed at a temperature between nor- 

